1. Field of the Invention
The present invention relates to a controlling method adapted for use in a homoepitaxial treatment for a monocrystalline film of silicon or the like on a silicon substrate (Si/Si), wherein the monocrystalline film of silicon is controlled in thickness at the time of its growth.
2. Description of the Prior Art
A substrate of structure in which an epitaxial growth layer (Ep-layer) is formed on a substrate of sapphire or silicon by a vapor growth is used as a substrate for forming semiconductor element therein from the viewpoint of improving their property. In this case, the Ep-layer is required to have a uniform thickness, for example, 1.6 .mu.m.+-.0.1 .mu.m in the Ep-layer for a bipolar memory.
In this respect, the Ep-layer must be monitored in thickness. In a heteroepitaxial treatment such as an Ep-layer of silicon on sapphire, the thickness of the Ep-layer has conventionally been monitored at the time of its growth.
In order to apply such a method to practice in a homoepitaxial treatment such as an Ep-layer of silicon on silicon (Si/Si), it is necessary to employ a dummy substrate made of sapphire, polycrystalline silicon or the like which differs in property from a silicon substrate, considering that the substrate has the same optical property (refractive index, absorption coefficient) as the Ep-layer. The Ep-layer on the silicon substrate, however, has a speed of growth different from that of the Ep-layer on the dummy substrate (sapphire or polycrystalline silicon). Further, particularly in the case of a sapphire substrate, impurities contained in sapphire are apt to out-diffuse in an ambient atmosphere whereby contamination of the epitaxial layer occurs.